1. Field of the Invention
The present invention relates to a nuclear magnetic resonance apparatus of Fourier transform type, which has a simple structure and can enjoy a high efficiency.
2. Description of the Prior Art
In order to obtain a spectrum of energy absorption due to the nuclear magnetic resonance phenomenon caused in a sample placed in an intense magnetic field, there are usually used two artifices: the frequency sweep method in which the h-f field applied to the sample is swept through nuclear resonant values and the magnetic field sweep method in which the intense field the sample is placed in is swept through nuclear resonant values. According to these methods, however, the resonance signal obtained by a single sweep is too weak to be observed so that the speed of sweep must be slow and the sweep must be repeated several times in order to obtain a signal observable enough. This takes a very long time for measurement, e.g. several tens of hours in a certain measurement case.
On the other hand, there is a method proposed to shorten the time taken in the measurement. According to the method, an h-f impulse field is repeatedly applied to a sample and the resonance signal induced as a result is subjected to Fourier transform to produce a resonance absorption spectrum. This method has on the one hand a great advantage since it needs rather a short time for measurement, but on the other hand, it has a drawback in a sense of economy since a conventional device used in it to perform the Fourier transform is usually an electronic computer which is very expensive. Namely, half the price of nuclear magnetic resonance apparatus using an electronic computer as the Fourier transform device was usually ascribed to the computer itself. Accordingly, there has been a great demand for a nuclear magnetic resonance apparatus which is not furnished with an electronic computer and therefore inexpensive and which can attain an efficiency higher than with a nuclear magnetic resonance apparatus using an electronic computer. In order to meet this requirement, the inventors have designed and employed anew a circuit to perform the Fourier transform in an analog fashion, which is constituted only of inexpensive analog IC elements sold on the market, instead of using an electronic computer serving as a conventional Fourier transform device operating digitally.